Problem: $ { {4} \times \left[\begin{array}{rr}{-1} & {1} \\ {4} & {2}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{4}\times{-1} & {4}\times{1} \\ {4}\times{4} & {4}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-4} & {4} \\ {16} & {8}\end{array}\right]}$